Definition of pinacoidal in US English:

pinacoidal

adjective

  • Of the nature of or relating to a pinacoid; = pinacoid; specifically designating a triclinic crystal form having a centre of symmetry; (of cleavage) occurring parallel to one of the pinacoidal surfaces of a crystal.

Origin

Late 19th century; earliest use found in Frank Rutley (1842–1904), geologist. From pinacoid + -al.

Pronunciation

pinacoidal

/pɪnəˈkɔɪdl/